<!DOCTYPE html>



  


<html class="theme-next gemini use-motion" lang="zh-Hans">
<head>
  <meta charset="UTF-8"/>
<meta http-equiv="X-UA-Compatible" content="IE=edge" />
<meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1"/>
<meta name="theme-color" content="#222">









<meta http-equiv="Cache-Control" content="no-transform" />
<meta http-equiv="Cache-Control" content="no-siteapp" />
















  
  
  <link href="/blog/lib/fancybox/source/jquery.fancybox.css?v=2.1.5" rel="stylesheet" type="text/css" />







<link href="/blog/lib/font-awesome/css/font-awesome.min.css?v=4.6.2" rel="stylesheet" type="text/css" />

<link href="/blog/css/main.css?v=5.1.4" rel="stylesheet" type="text/css" />



  <link rel="icon" type="image/png" sizes="32x32" href="http://toly1994328.gitee.io/photo/base/icon_head_32x32.png?v=5.1.4">


  <link rel="icon" type="image/png" sizes="16x16" href="http://toly1994328.gitee.io/photo/base/icon_head_32x32.png?v=5.1.4">






  <meta name="keywords" content="widget,布局型组件," />










<meta name="description" content="一、认识组件1.PreferredSize组件介绍 实现了PreferredSizeWidget接口，可容纳一个子组件，设置优先尺寸，不会对其子组件施加任何约束。">
<meta property="og:type" content="article">
<meta property="og:title" content="PreferredSize优先尺寸">
<meta property="og:url" content="http://toly1994328.gitee.io/PreferredSize.html">
<meta property="og:site_name" content="张风捷特烈">
<meta property="og:description" content="一、认识组件1.PreferredSize组件介绍 实现了PreferredSizeWidget接口，可容纳一个子组件，设置优先尺寸，不会对其子组件施加任何约束。">
<meta property="og:image" content="http://toly1994328.gitee.io/photo/flutter/unit/widgets/PreferredSize/01.png">
<meta property="og:image" content="http://toly1994328.gitee.io/photo/flutter/unit/widgets/PreferredSize/02.png">
<meta property="og:image" content="http://toly1994328.gitee.io/photo/flutter/unit/widgets/PreferredSize/01.png">
<meta property="article:published_time" content="2020-05-03T05:46:25.000Z">
<meta property="article:modified_time" content="2020-05-03T05:05:23.000Z">
<meta property="article:author" content="张风捷特烈">
<meta property="article:tag" content="widget">
<meta property="article:tag" content="布局型组件">
<meta name="twitter:card" content="summary">
<meta name="twitter:image" content="http://toly1994328.gitee.io/photo/flutter/unit/widgets/PreferredSize/01.png">



<script type="text/javascript" id="hexo.configurations">
  var NexT = window.NexT || {};
  var CONFIG = {
    root: '/blog/',
    scheme: 'Gemini',
    version: '5.1.4',
    sidebar: {"position":"left","display":"post","offset":12,"b2t":false,"scrollpercent":false,"onmobile":false},
    fancybox: true,
    tabs: true,
    motion: {"enable":true,"async":false,"transition":{"post_block":"fadeIn","post_header":"slideDownIn","post_body":"slideDownIn","coll_header":"slideLeftIn","sidebar":"slideUpIn"}},
    duoshuo: {
      userId: '0',
      author: '博主'
    },
    algolia: {
      applicationID: '',
      apiKey: '',
      indexName: '',
      hits: {"per_page":10},
      labels: {"input_placeholder":"Search for Posts","hits_empty":"We didn't find any results for the search: ${query}","hits_stats":"${hits} results found in ${time} ms"}
    }
  };
</script>



  <link rel="canonical" href="http://toly1994328.gitee.io/PreferredSize.html"/>





  <title>PreferredSize优先尺寸 | 张风捷特烈</title>
  








<meta name="generator" content="Hexo 4.2.0"></head>

<body itemscope itemtype="http://schema.org/WebPage" lang="zh-Hans">

  
  
    
  

  <div class="container sidebar-position-left page-post-detail">
    <div class="headband"></div>
<a href="https://github.com/toly1994328" target="_blank" rel="noopener" class="github-corner" aria-label="View source on GitHub"><svg width="80" height="80" viewBox="0 0 250 250" style="fill:#151513; color:#fff; position: absolute; top: 0; border: 0; right: 0;" aria-hidden="true"><path d="M0,0 L115,115 L130,115 L142,142 L250,250 L250,0 Z"></path><path d="M128.3,109.0 C113.8,99.7 119.0,89.6 119.0,89.6 C122.0,82.7 120.5,78.6 120.5,78.6 C119.2,72.0 123.4,76.3 123.4,76.3 C127.3,80.9 125.5,87.3 125.5,87.3 C122.9,97.6 130.6,101.9 134.4,103.2" fill="currentColor" style="transform-origin: 130px 106px;" class="octo-arm"></path><path d="M115.0,115.0 C114.9,115.1 118.7,116.5 119.8,115.4 L133.7,101.6 C136.9,99.2 139.9,98.4 142.2,98.6 C133.8,88.0 127.5,74.4 143.8,58.0 C148.5,53.4 154.0,51.2 159.7,51.0 C160.3,49.4 163.2,43.6 171.4,40.1 C171.4,40.1 176.1,42.5 178.8,56.2 C183.1,58.6 187.2,61.8 190.9,65.4 C194.5,69.0 197.7,73.2 200.1,77.6 C213.8,80.2 216.3,84.9 216.3,84.9 C212.7,93.1 206.9,96.0 205.4,96.6 C205.1,102.4 203.0,107.8 198.3,112.5 C181.9,128.9 168.3,122.5 157.7,114.1 C157.9,116.9 156.7,120.9 152.7,124.9 L141.0,136.5 C139.8,137.7 141.6,141.9 141.8,141.8 Z" fill="currentColor" class="octo-body"></path></svg></a><style>.github-corner:hover .octo-arm{animation:octocat-wave 560ms ease-in-out}@keyframes octocat-wave{0%,100%{transform:rotate(0)}20%,60%{transform:rotate(-25deg)}40%,80%{transform:rotate(10deg)}}@media (max-width:500px){.github-corner:hover .octo-arm{animation:none}.github-corner .octo-arm{animation:octocat-wave 560ms ease-in-out}}</style>
    <header id="header" class="header" itemscope itemtype="http://schema.org/WPHeader">
      <div class="header-inner"><div class="site-brand-wrapper">
  <div class="site-meta ">
    

    <div class="custom-logo-site-title">
      <a href="/blog/"  class="brand" rel="start">
        <span class="logo-line-before"><i></i></span>
        <span class="site-title">张风捷特烈</span>
        <span class="logo-line-after"><i></i></span>
      </a>
    </div>
      
        <p class="site-subtitle"></p>
      
  </div>

  <div class="site-nav-toggle">
    <button>
      <span class="btn-bar"></span>
      <span class="btn-bar"></span>
      <span class="btn-bar"></span>
    </button>
  </div>
</div>

<nav class="site-nav">
  

  
    <ul id="menu" class="menu">
      
        
        <li class="menu-item menu-item-home">
          <a href="/blog/" rel="section">
            
              <i class="menu-item-icon fa fa-fw fa-home"></i> <br />
            
            首页
          </a>
        </li>
      
        
        <li class="menu-item menu-item-tags">
          <a href="/blog/tags/" rel="section">
            
              <i class="menu-item-icon fa fa-fw fa-tags"></i> <br />
            
            标签
          </a>
        </li>
      
        
        <li class="menu-item menu-item-categories">
          <a href="/blog/categories/" rel="section">
            
              <i class="menu-item-icon fa fa-fw fa-th"></i> <br />
            
            分类
          </a>
        </li>
      
        
        <li class="menu-item menu-item-archives">
          <a href="/blog/archives/" rel="section">
            
              <i class="menu-item-icon fa fa-fw fa-archive"></i> <br />
            
            归档
          </a>
        </li>
      
        
        <li class="menu-item menu-item-schedule">
          <a href="/blog/schedule/" rel="section">
            
              <i class="menu-item-icon fa fa-fw fa-calendar"></i> <br />
            
            日程表
          </a>
        </li>
      

      
        <li class="menu-item menu-item-search">
          
            <a href="javascript:;" class="popup-trigger">
          
            
              <i class="menu-item-icon fa fa-search fa-fw"></i> <br />
            
            搜索
          </a>
        </li>
      
    </ul>
  

  
    <div class="site-search">
      
  <div class="popup search-popup local-search-popup">
  <div class="local-search-header clearfix">
    <span class="search-icon">
      <i class="fa fa-search"></i>
    </span>
    <span class="popup-btn-close">
      <i class="fa fa-times-circle"></i>
    </span>
    <div class="local-search-input-wrapper">
      <input autocomplete="off"
             placeholder="搜索..." spellcheck="false"
             type="text" id="local-search-input">
    </div>
  </div>
  <div id="local-search-result"></div>
</div>



    </div>
  
</nav>



 </div>
    </header>

    <main id="main" class="main">
      <div class="main-inner">
        <div class="content-wrap">
          <div id="content" class="content">
            

  <div id="posts" class="posts-expand">
    

  

  
  
  

  <article class="post post-type-normal" itemscope itemtype="http://schema.org/Article">
  
  
  
  <div class="post-block">
    <link itemprop="mainEntityOfPage" href="http://toly1994328.gitee.io/blog/PreferredSize.html">

    <span hidden itemprop="author" itemscope itemtype="http://schema.org/Person">
      <meta itemprop="name" content="张风捷特烈">
      <meta itemprop="description" content="">
      <meta itemprop="image" content="http://toly1994328.gitee.io/photo/base/icon_head.png">
    </span>

    <span hidden itemprop="publisher" itemscope itemtype="http://schema.org/Organization">
      <meta itemprop="name" content="张风捷特烈">
    </span>

    
      <header class="post-header">

        
        
          <h1 class="post-title" itemprop="name headline">PreferredSize优先尺寸</h1>
        

        <div class="post-meta">
          <span class="post-time">
            
              <span class="post-meta-item-icon">
                <i class="fa fa-calendar-o"></i>
              </span>
              
                <span class="post-meta-item-text">发表于</span>
              
              <time title="创建于" itemprop="dateCreated datePublished" datetime="2020-05-03T13:46:25+08:00">
                2020-05-03
              </time>
            

            

            
          </span>

          
            <span class="post-category" >
            
              <span class="post-meta-divider">|</span>
            
              <span class="post-meta-item-icon">
                <i class="fa fa-folder-o"></i>
              </span>
              
                <span class="post-meta-item-text">分类于</span>
              
              
                <span itemprop="about" itemscope itemtype="http://schema.org/Thing">
                  <a href="/blog/categories/Flutter%E7%BB%84%E4%BB%B6/" itemprop="url" rel="index">
                    <span itemprop="name">Flutter组件</span>
                  </a>
                </span>

                
                
              
            </span>
          

          
            
          

          
          

          

          
            <div class="post-wordcount">
              
                
                <span class="post-meta-item-icon">
                  <i class="fa fa-file-word-o"></i>
                </span>
                
                  <span class="post-meta-item-text">字数统计&#58;</span>
                
                <span title="字数统计">
                  367
                </span>
              

              
                <span class="post-meta-divider">|</span>
              

              
                <span class="post-meta-item-icon">
                  <i class="fa fa-clock-o"></i>
                </span>
                
                  <span class="post-meta-item-text">阅读时长 &asymp;</span>
                
                <span title="阅读时长">
                  1
                </span>
              
            </div>
          

          

        </div>
      </header>
    

    
    
    
    <div class="post-body" itemprop="articleBody">

      
      

      
        <h4 id="一、认识组件"><a href="#一、认识组件" class="headerlink" title="一、认识组件"></a>一、认识组件</h4><h5 id="1-PreferredSize组件介绍"><a href="#1-PreferredSize组件介绍" class="headerlink" title="1.PreferredSize组件介绍"></a>1.PreferredSize组件介绍</h5><blockquote>
<p>实现了PreferredSizeWidget接口，可容纳一个子组件，设置优先尺寸，不会对其子组件施加任何约束。</p>
</blockquote>
<p><img src="http://toly1994328.gitee.io/photo/flutter/unit/widgets/PreferredSize/01.png" alt=""></p>
<a id="more"></a>

<figure class="highlight makefile"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="section">名称:       PreferredSize  优先尺寸</span></span><br><span class="line"><span class="section">类型:       布局型</span></span><br><span class="line"><span class="section">重要性:     ☆☆</span></span><br><span class="line"><span class="section">相关组件:   【Scaffold】、【AppBar】    </span></span><br><span class="line"><span class="section">家族:       Widget</span></span><br><span class="line">                |--- StatelessWidget</span><br><span class="line">                |--- PreferredSizeWidget</span><br></pre></td></tr></table></figure>

<hr>
<h5 id="2-组件属性一览"><a href="#2-组件属性一览" class="headerlink" title="2. 组件属性一览"></a>2. 组件属性一览</h5><table>
<thead>
<tr>
<th>属性名</th>
<th>属性类型</th>
<th>默认值</th>
<th>备注</th>
</tr>
</thead>
<tbody><tr>
<td>key</td>
<td>Key</td>
<td>null</td>
<td>组件键</td>
</tr>
<tr>
<td>preferredSize</td>
<td>Size</td>
<td>@required</td>
<td>优先尺寸</td>
</tr>
<tr>
<td>child</td>
<td>Widget</td>
<td>@required</td>
<td>子组件</td>
</tr>
</tbody></table>
<blockquote>
<p>也许你曾为<code>Scaffold的appBar是PreferredSizeWidget</code>而束手无策，只能用AppBar<br><code>PreferredSize</code>可以将一个普通的组件转化成<code>PreferredSizeWidget</code></p>
</blockquote>
<hr>
<h4 id="二、使用组件"><a href="#二、使用组件" class="headerlink" title="二、使用组件"></a>二、使用组件</h4><h5 id="1-修改AppBar高度"><a href="#1-修改AppBar高度" class="headerlink" title="1. 修改AppBar高度"></a>1. 修改AppBar高度</h5><blockquote>
<p> AppBar高度的默认高度是<code>56.0</code>，使用PreferredSize可以进行调整</p>
</blockquote>
<figure class="highlight angelscript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/// The height of the toolbar component of the [AppBar].</span></span><br><span class="line"><span class="keyword">const</span> <span class="built_in">double</span> kToolbarHeight = <span class="number">56.0</span>;</span><br></pre></td></tr></table></figure>


<p><img src="http://toly1994328.gitee.io/photo/flutter/unit/widgets/PreferredSize/02.png" alt=""></p>
<figure class="highlight scala"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br></pre></td><td class="code"><pre><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">CustomPreferredSize</span> <span class="keyword">extends</span> <span class="title">StatelessWidget</span> </span>&#123;</span><br><span class="line">  <span class="meta">@override</span></span><br><span class="line">  <span class="type">Widget</span> build(<span class="type">BuildContext</span> context) &#123;</span><br><span class="line">    <span class="keyword">return</span> <span class="type">Container</span>(</span><br><span class="line">      height: <span class="number">200</span>,</span><br><span class="line">      child: <span class="type">Scaffold</span>(</span><br><span class="line">        appBar: <span class="type">PreferredSize</span>(</span><br><span class="line">          preferredSize: <span class="type">Size</span>.fromHeight(<span class="number">150</span>),</span><br><span class="line">          child: <span class="type">AppBar</span>(</span><br><span class="line">            title: <span class="type">Text</span>(<span class="symbol">'PreferredSiz</span>e'),</span><br><span class="line">          ),</span><br><span class="line">        ),</span><br><span class="line">      ),</span><br><span class="line">    );</span><br><span class="line">  &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<hr>
<h5 id="2-将普通组件转化成PreferredSizeWidget"><a href="#2-将普通组件转化成PreferredSizeWidget" class="headerlink" title="2. 将普通组件转化成PreferredSizeWidget"></a>2. 将普通组件转化成<code>PreferredSizeWidget</code></h5><blockquote>
<p>当你遇到属性是<code>PreferredSizeWidget</code>时，你只能去找PreferredSizeWidget的实现类<br>这样限制会很大，如AppBar的底部栏，可以用PreferredSize包裹一下，容纳任何组件</p>
</blockquote>
<p><img src="http://toly1994328.gitee.io/photo/flutter/unit/widgets/PreferredSize/01.png" alt=""></p>
<figure class="highlight less"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br></pre></td><td class="code"><pre><span class="line"><span class="selector-tag">class</span> <span class="selector-tag">PaddingOnly</span> <span class="selector-tag">extends</span> <span class="selector-tag">StatelessWidget</span> &#123;</span><br><span class="line"></span><br><span class="line">  <span class="variable">@override</span></span><br><span class="line">  Widget build(BuildContext context) &#123;</span><br><span class="line">    <span class="selector-tag">return</span> <span class="selector-tag">Container</span>(</span><br><span class="line">      <span class="attribute">color</span>: Colors.grey.withAlpha(<span class="number">22</span>),</span><br><span class="line">      <span class="attribute">width</span>: <span class="number">200</span>,</span><br><span class="line">      <span class="attribute">height</span>: <span class="number">150</span>,</span><br><span class="line">      <span class="attribute">child</span>: Padding(</span><br><span class="line">        <span class="attribute">padding</span>: EdgeInsets.only(<span class="attribute">top</span>:<span class="number">10</span>,<span class="attribute">left</span>: <span class="number">10</span>),</span><br><span class="line">        <span class="attribute">child</span>: _buildChild(),</span><br><span class="line">      ),</span><br><span class="line">    );</span><br><span class="line">  &#125;</span><br><span class="line"></span><br><span class="line">  <span class="selector-tag">Widget</span> <span class="selector-tag">_buildChild</span>() &#123;</span><br><span class="line">    <span class="selector-tag">return</span> <span class="selector-tag">Container</span>(</span><br><span class="line">      <span class="attribute">alignment</span>: Alignment.center,</span><br><span class="line">      <span class="attribute">color</span>: Colors.cyanAccent,</span><br><span class="line">      <span class="attribute">width</span>: <span class="number">100</span>,</span><br><span class="line">      <span class="attribute">height</span>: <span class="number">100</span>,</span><br><span class="line">      <span class="attribute">child</span>: Text(<span class="string">"孩子"</span>),</span><br><span class="line">    );</span><br><span class="line">  &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>





<hr>
<h4 id="三、尾声"><a href="#三、尾声" class="headerlink" title="三、尾声"></a>三、尾声</h4><blockquote>
<p> FlutterUnit开源项目: <a href="https://github.com/toly1994328/FlutterUnit" target="_blank" rel="noopener">https://github.com/toly1994328/FlutterUnit</a><br>我的公众号:编程之王<br>联系我–邮箱:<a href="mailto:1981462002@qq.com">1981462002@qq.com</a> –微信:zdl1994328<br>@张风捷特烈 2020.04.29<br>~ END ~</p>
</blockquote>

      
    </div>
    
    
    

    
      <div>
        <div id="wechat_subscriber" style="display: block; padding: 10px 0; margin: 20px auto; width: 100%; text-align: center">
    <img id="wechat_subscriber_qcode" src="/images/ewm.png" alt="张风捷特烈 wechat" style="width: 200px; max-width: 100%;"/>
    <div></div>
</div>

      </div>
    

    
      <div>
        <div style="padding: 10px 0; margin: 20px auto; width: 90%; text-align: center;">
  <div></div>
  <button id="rewardButton" disable="enable" onclick="var qr = document.getElementById('QR'); if (qr.style.display === 'none') {qr.style.display='block';} else {qr.style.display='none'}">
    <span>打赏</span>
  </button>
  <div id="QR" style="display: none;">

    
      <div id="wechat" style="display: inline-block">
        <img id="wechat_qr" src="/images/wei_x.jpg" alt="张风捷特烈 微信支付"/>
        <p>微信支付</p>
      </div>
    

    
      <div id="alipay" style="display: inline-block">
        <img id="alipay_qr" src="/images/alipay.jpg" alt="张风捷特烈 支付宝"/>
        <p>支付宝</p>
      </div>
    

    

  </div>
</div>

      </div>
    

    

<div>
    
        <div style="text-align:center;color: #ccc;font-size:14px;">-------------本文结束<i class="fa fa-paw"></i>感谢您的阅读 @张风捷特烈-------------</div>
    
</div>

    <footer class="post-footer">
      
        <div class="post-tags">
          
            <a href="/blog/tags/widget/" rel="tag"><i class="fa fa-tag"></i> widget</a>
          
            <a href="/blog/tags/%E5%B8%83%E5%B1%80%E5%9E%8B%E7%BB%84%E4%BB%B6/" rel="tag"><i class="fa fa-tag"></i> 布局型组件</a>
          
        </div>
      



      
      
      

      
        <div class="post-nav">
          <div class="post-nav-next post-nav-item">
            
              <a href="/blog/Padding.html" rel="next" title="Padding内边距组件">
                <i class="fa fa-chevron-left"></i> Padding内边距组件
              </a>
            
          </div>

          <span class="post-nav-divider"></span>

          <div class="post-nav-prev post-nav-item">
            
          </div>
        </div>
      

      
      
    </footer>
  </div>
  
  
  
  </article>



    <div class="post-spread">
      
    </div>
  </div>


          </div>
          


          

  



        </div>
        
          
  
  <div class="sidebar-toggle">
    <div class="sidebar-toggle-line-wrap">
      <span class="sidebar-toggle-line sidebar-toggle-line-first"></span>
      <span class="sidebar-toggle-line sidebar-toggle-line-middle"></span>
      <span class="sidebar-toggle-line sidebar-toggle-line-last"></span>
    </div>
  </div>

  <aside id="sidebar" class="sidebar">
    
    <div class="sidebar-inner">

      

      
        <ul class="sidebar-nav motion-element">
          <li class="sidebar-nav-toc sidebar-nav-active" data-target="post-toc-wrap">
            文章目录
          </li>
          <li class="sidebar-nav-overview" data-target="site-overview-wrap">
            站点概览
          </li>
        </ul>
      

      <section class="site-overview-wrap sidebar-panel">
        <div class="site-overview">
          <div class="site-author motion-element" itemprop="author" itemscope itemtype="http://schema.org/Person">
            
              <img class="site-author-image" itemprop="image"
                src="http://toly1994328.gitee.io/photo/base/icon_head.png"
                alt="张风捷特烈" />
            
              <p class="site-author-name" itemprop="name">张风捷特烈</p>
              <p class="site-description motion-element" itemprop="description"></p>
          </div>

          <nav class="site-state motion-element">

            
              <div class="site-state-item site-state-posts">
              
                <a href="/blog/archives/">
              
                  <span class="site-state-item-count">6</span>
                  <span class="site-state-item-name">日志</span>
                </a>
              </div>
            

            
              
              
              <div class="site-state-item site-state-categories">
                <a href="/blog/categories/index.html">
                  <span class="site-state-item-count">2</span>
                  <span class="site-state-item-name">分类</span>
                </a>
              </div>
            

            
              
              
              <div class="site-state-item site-state-tags">
                <a href="/blog/tags/index.html">
                  <span class="site-state-item-count">4</span>
                  <span class="site-state-item-name">标签</span>
                </a>
              </div>
            

          </nav>

          

          
            <div class="links-of-author motion-element">
                
                  <span class="links-of-author-item">
                    <a href="https://github.com/toly1994328" target="_blank" title="GitHub">
                      
                        <i class="fa fa-fw fa-github"></i></a>
                  </span>
                
                  <span class="links-of-author-item">
                    <a href="https://juejin.im/user/5b42c0656fb9a04fe727eb37" target="_blank" title="E-Mail">
                      
                        <i class="fa fa-fw fa-envelope"></i></a>
                  </span>
                
            </div>
          

          
          

          
          

          

        </div>
      </section>

      
      <!--noindex-->
        <section class="post-toc-wrap motion-element sidebar-panel sidebar-panel-active">
          <div class="post-toc">

            
              
            

            
              <div class="post-toc-content"><ol class="nav"><li class="nav-item nav-level-4"><a class="nav-link" href="#一、认识组件"><span class="nav-number">1.</span> <span class="nav-text">一、认识组件</span></a><ol class="nav-child"><li class="nav-item nav-level-5"><a class="nav-link" href="#1-PreferredSize组件介绍"><span class="nav-number">1.1.</span> <span class="nav-text">1.PreferredSize组件介绍</span></a></li><li class="nav-item nav-level-5"><a class="nav-link" href="#2-组件属性一览"><span class="nav-number">1.2.</span> <span class="nav-text">2. 组件属性一览</span></a></li></ol></li><li class="nav-item nav-level-4"><a class="nav-link" href="#二、使用组件"><span class="nav-number">2.</span> <span class="nav-text">二、使用组件</span></a><ol class="nav-child"><li class="nav-item nav-level-5"><a class="nav-link" href="#1-修改AppBar高度"><span class="nav-number">2.1.</span> <span class="nav-text">1. 修改AppBar高度</span></a></li><li class="nav-item nav-level-5"><a class="nav-link" href="#2-将普通组件转化成PreferredSizeWidget"><span class="nav-number">2.2.</span> <span class="nav-text">2. 将普通组件转化成PreferredSizeWidget</span></a></li></ol></li><li class="nav-item nav-level-4"><a class="nav-link" href="#三、尾声"><span class="nav-number">3.</span> <span class="nav-text">三、尾声</span></a></li></ol></div>
            

          </div>
        </section>
      <!--/noindex-->
      

      

    </div>
  </aside>


        
      </div>
    </main>

    <footer id="footer" class="footer">
      <div class="footer-inner">
        <script async src="https://busuanzi.ibruce.info/busuanzi/2.3/busuanzi.pure.mini.js"></script>
<div class="copyright">&copy; <span itemprop="copyrightYear">2020</span>
    <span class="post-meta-divider">|</span>
  <span class="with-love">
    <i class="fa fa-user"></i>
  </span>
  <a class="theme-link" target="_blank" href="https://github.com/toly1994328/toly1994328.github.io">@张风捷特烈</a>
      <span class="post-meta-divider">|</span>
    <i class="fa fa-user-md"></i><span id="busuanzi_container_site_uv">
      访客数:<span id="busuanzi_value_site_uv"></span>
    </span>
    <span class="post-meta-divider">|</span>
    <div class="theme-info">
              <div class="powered-by"></div>
              <span class="post-count">全站共2.7k字</span>
            </div>
</div>


<div class='beian'>
<a href="http://www.beian.miit.gov.cn/" target="_blank" rel="nofollow">皖ICP备18001618号-2</a>
    <span class="post-meta-divider">|</span>
</span> <a class='beian-img' href="http://www.beian.gov.cn/portal/registerSystemInfo?recordcode=34010202600392" target="_blank" rel="nofollow">
<img src="/images/beian.png" alt=""> &nbsp; 皖公网安备 34010202600392号</a>
</div>






        







        
      </div>
    </footer>

    
      <div class="back-to-top">
        <i class="fa fa-arrow-up"></i>
        
      </div>
    

    

  </div>

  

<script type="text/javascript">
  if (Object.prototype.toString.call(window.Promise) !== '[object Function]') {
    window.Promise = null;
  }
</script>









  


  











  
  
    <script type="text/javascript" src="/blog/lib/jquery/index.js?v=2.1.3"></script>
  

  
  
    <script type="text/javascript" src="/blog/lib/fastclick/lib/fastclick.min.js?v=1.0.6"></script>
  

  
  
    <script type="text/javascript" src="/blog/lib/jquery_lazyload/jquery.lazyload.js?v=1.9.7"></script>
  

  
  
    <script type="text/javascript" src="/blog/lib/velocity/velocity.min.js?v=1.2.1"></script>
  

  
  
    <script type="text/javascript" src="/blog/lib/velocity/velocity.ui.min.js?v=1.2.1"></script>
  

  
  
    <script type="text/javascript" src="/blog/lib/fancybox/source/jquery.fancybox.pack.js?v=2.1.5"></script>
  

  
  
    <script type="text/javascript" src="/blog/lib/canvas-nest/canvas-nest.min.js"></script>
  


  


  <script type="text/javascript" src="/blog/js/src/utils.js?v=5.1.4"></script>

  <script type="text/javascript" src="/blog/js/src/motion.js?v=5.1.4"></script>



  
  


  <script type="text/javascript" src="/blog/js/src/affix.js?v=5.1.4"></script>

  <script type="text/javascript" src="/blog/js/src/schemes/pisces.js?v=5.1.4"></script>



  
  <script type="text/javascript" src="/blog/js/src/scrollspy.js?v=5.1.4"></script>
<script type="text/javascript" src="/blog/js/src/post-details.js?v=5.1.4"></script>



  


  <script type="text/javascript" src="/blog/js/src/bootstrap.js?v=5.1.4"></script>



  


  




	





  





  












  

  <script type="text/javascript">
    // Popup Window;
    var isfetched = false;
    var isXml = true;
    // Search DB path;
    var search_path = "search.xml";
    if (search_path.length === 0) {
      search_path = "search.xml";
    } else if (/json$/i.test(search_path)) {
      isXml = false;
    }
    var path = "/blog/" + search_path;
    // monitor main search box;

    var onPopupClose = function (e) {
      $('.popup').hide();
      $('#local-search-input').val('');
      $('.search-result-list').remove();
      $('#no-result').remove();
      $(".local-search-pop-overlay").remove();
      $('body').css('overflow', '');
    }

    function proceedsearch() {
      $("body")
        .append('<div class="search-popup-overlay local-search-pop-overlay"></div>')
        .css('overflow', 'hidden');
      $('.search-popup-overlay').click(onPopupClose);
      $('.popup').toggle();
      var $localSearchInput = $('#local-search-input');
      $localSearchInput.attr("autocapitalize", "none");
      $localSearchInput.attr("autocorrect", "off");
      $localSearchInput.focus();
    }

    // search function;
    var searchFunc = function(path, search_id, content_id) {
      'use strict';

      // start loading animation
      $("body")
        .append('<div class="search-popup-overlay local-search-pop-overlay">' +
          '<div id="search-loading-icon">' +
          '<i class="fa fa-spinner fa-pulse fa-5x fa-fw"></i>' +
          '</div>' +
          '</div>')
        .css('overflow', 'hidden');
      $("#search-loading-icon").css('margin', '20% auto 0 auto').css('text-align', 'center');

      $.ajax({
        url: path,
        dataType: isXml ? "xml" : "json",
        async: true,
        success: function(res) {
          // get the contents from search data
          isfetched = true;
          $('.popup').detach().appendTo('.header-inner');
          var datas = isXml ? $("entry", res).map(function() {
            return {
              title: $("title", this).text(),
              content: $("content",this).text(),
              url: $("url" , this).text()
            };
          }).get() : res;
          var input = document.getElementById(search_id);
          var resultContent = document.getElementById(content_id);
          var inputEventFunction = function() {
            var searchText = input.value.trim().toLowerCase();
            var keywords = searchText.split(/[\s\-]+/);
            if (keywords.length > 1) {
              keywords.push(searchText);
            }
            var resultItems = [];
            if (searchText.length > 0) {
              // perform local searching
              datas.forEach(function(data) {
                var isMatch = false;
                var hitCount = 0;
                var searchTextCount = 0;
                var title = data.title.trim();
                var titleInLowerCase = title.toLowerCase();
                var content = data.content.trim().replace(/<[^>]+>/g,"");
                var contentInLowerCase = content.toLowerCase();
                var articleUrl = decodeURIComponent(data.url);
                var indexOfTitle = [];
                var indexOfContent = [];
                // only match articles with not empty titles
                if(title != '') {
                  keywords.forEach(function(keyword) {
                    function getIndexByWord(word, text, caseSensitive) {
                      var wordLen = word.length;
                      if (wordLen === 0) {
                        return [];
                      }
                      var startPosition = 0, position = [], index = [];
                      if (!caseSensitive) {
                        text = text.toLowerCase();
                        word = word.toLowerCase();
                      }
                      while ((position = text.indexOf(word, startPosition)) > -1) {
                        index.push({position: position, word: word});
                        startPosition = position + wordLen;
                      }
                      return index;
                    }

                    indexOfTitle = indexOfTitle.concat(getIndexByWord(keyword, titleInLowerCase, false));
                    indexOfContent = indexOfContent.concat(getIndexByWord(keyword, contentInLowerCase, false));
                  });
                  if (indexOfTitle.length > 0 || indexOfContent.length > 0) {
                    isMatch = true;
                    hitCount = indexOfTitle.length + indexOfContent.length;
                  }
                }

                // show search results

                if (isMatch) {
                  // sort index by position of keyword

                  [indexOfTitle, indexOfContent].forEach(function (index) {
                    index.sort(function (itemLeft, itemRight) {
                      if (itemRight.position !== itemLeft.position) {
                        return itemRight.position - itemLeft.position;
                      } else {
                        return itemLeft.word.length - itemRight.word.length;
                      }
                    });
                  });

                  // merge hits into slices

                  function mergeIntoSlice(text, start, end, index) {
                    var item = index[index.length - 1];
                    var position = item.position;
                    var word = item.word;
                    var hits = [];
                    var searchTextCountInSlice = 0;
                    while (position + word.length <= end && index.length != 0) {
                      if (word === searchText) {
                        searchTextCountInSlice++;
                      }
                      hits.push({position: position, length: word.length});
                      var wordEnd = position + word.length;

                      // move to next position of hit

                      index.pop();
                      while (index.length != 0) {
                        item = index[index.length - 1];
                        position = item.position;
                        word = item.word;
                        if (wordEnd > position) {
                          index.pop();
                        } else {
                          break;
                        }
                      }
                    }
                    searchTextCount += searchTextCountInSlice;
                    return {
                      hits: hits,
                      start: start,
                      end: end,
                      searchTextCount: searchTextCountInSlice
                    };
                  }

                  var slicesOfTitle = [];
                  if (indexOfTitle.length != 0) {
                    slicesOfTitle.push(mergeIntoSlice(title, 0, title.length, indexOfTitle));
                  }

                  var slicesOfContent = [];
                  while (indexOfContent.length != 0) {
                    var item = indexOfContent[indexOfContent.length - 1];
                    var position = item.position;
                    var word = item.word;
                    // cut out 100 characters
                    var start = position - 20;
                    var end = position + 80;
                    if(start < 0){
                      start = 0;
                    }
                    if (end < position + word.length) {
                      end = position + word.length;
                    }
                    if(end > content.length){
                      end = content.length;
                    }
                    slicesOfContent.push(mergeIntoSlice(content, start, end, indexOfContent));
                  }

                  // sort slices in content by search text's count and hits' count

                  slicesOfContent.sort(function (sliceLeft, sliceRight) {
                    if (sliceLeft.searchTextCount !== sliceRight.searchTextCount) {
                      return sliceRight.searchTextCount - sliceLeft.searchTextCount;
                    } else if (sliceLeft.hits.length !== sliceRight.hits.length) {
                      return sliceRight.hits.length - sliceLeft.hits.length;
                    } else {
                      return sliceLeft.start - sliceRight.start;
                    }
                  });

                  // select top N slices in content

                  var upperBound = parseInt('1');
                  if (upperBound >= 0) {
                    slicesOfContent = slicesOfContent.slice(0, upperBound);
                  }

                  // highlight title and content

                  function highlightKeyword(text, slice) {
                    var result = '';
                    var prevEnd = slice.start;
                    slice.hits.forEach(function (hit) {
                      result += text.substring(prevEnd, hit.position);
                      var end = hit.position + hit.length;
                      result += '<b class="search-keyword">' + text.substring(hit.position, end) + '</b>';
                      prevEnd = end;
                    });
                    result += text.substring(prevEnd, slice.end);
                    return result;
                  }

                  var resultItem = '';

                  if (slicesOfTitle.length != 0) {
                    resultItem += "<li><a href='" + articleUrl + "' class='search-result-title'>" + highlightKeyword(title, slicesOfTitle[0]) + "</a>";
                  } else {
                    resultItem += "<li><a href='" + articleUrl + "' class='search-result-title'>" + title + "</a>";
                  }

                  slicesOfContent.forEach(function (slice) {
                    resultItem += "<a href='" + articleUrl + "'>" +
                      "<p class=\"search-result\">" + highlightKeyword(content, slice) +
                      "...</p>" + "</a>";
                  });

                  resultItem += "</li>";
                  resultItems.push({
                    item: resultItem,
                    searchTextCount: searchTextCount,
                    hitCount: hitCount,
                    id: resultItems.length
                  });
                }
              })
            };
            if (keywords.length === 1 && keywords[0] === "") {
              resultContent.innerHTML = '<div id="no-result"><i class="fa fa-search fa-5x" /></div>'
            } else if (resultItems.length === 0) {
              resultContent.innerHTML = '<div id="no-result"><i class="fa fa-frown-o fa-5x" /></div>'
            } else {
              resultItems.sort(function (resultLeft, resultRight) {
                if (resultLeft.searchTextCount !== resultRight.searchTextCount) {
                  return resultRight.searchTextCount - resultLeft.searchTextCount;
                } else if (resultLeft.hitCount !== resultRight.hitCount) {
                  return resultRight.hitCount - resultLeft.hitCount;
                } else {
                  return resultRight.id - resultLeft.id;
                }
              });
              var searchResultList = '<ul class=\"search-result-list\">';
              resultItems.forEach(function (result) {
                searchResultList += result.item;
              })
              searchResultList += "</ul>";
              resultContent.innerHTML = searchResultList;
            }
          }

          if ('auto' === 'auto') {
            input.addEventListener('input', inputEventFunction);
          } else {
            $('.search-icon').click(inputEventFunction);
            input.addEventListener('keypress', function (event) {
              if (event.keyCode === 13) {
                inputEventFunction();
              }
            });
          }

          // remove loading animation
          $(".local-search-pop-overlay").remove();
          $('body').css('overflow', '');

          proceedsearch();
        }
      });
    }

    // handle and trigger popup window;
    $('.popup-trigger').click(function(e) {
      e.stopPropagation();
      if (isfetched === false) {
        searchFunc(path, 'local-search-input', 'local-search-result');
      } else {
        proceedsearch();
      };
    });

    $('.popup-btn-close').click(onPopupClose);
    $('.popup').click(function(e){
      e.stopPropagation();
    });
    $(document).on('keyup', function (event) {
      var shouldDismissSearchPopup = event.which === 27 &&
        $('.search-popup').is(':visible');
      if (shouldDismissSearchPopup) {
        onPopupClose();
      }
    });
  </script>





  

  

  

  
  

  

  

  

</body>
</html>
